Earth's molten mantle

Antiphon

I was watching Bill Nye the science guy on TV recently.

He stated that the earth's insides are molten because they were
really hot a long time ago and they just haven't cooled off yet.

We all know that's rubbish. It's the natural radioactive decay
of isotopes in the earth that keeps it hot.

Why is this guy misleading children this way?

I think it's because he doesn't want kids growing up to think that
radioactivity is as natural as sunshine and rain. He'd prefer them to
think its an evil byproduct of modern civilization.

What do YOU think?

Andre

Yes, the first is rubbish, but how true is the second?

Some interesting background on that:

http://www.me.ucsb.edu/dept_site/van...putational.pdf

theCandyman

Antiphon, what isotopes are decaying?

pallidin

All I know is that if I were the size and mass of the Earth, my core would be hot from compression. Eventually it would cool, but I would suppose it would take a great deal of time.

Antiphon

Well, not being a nuclear engineer I don't know authoritatively.
But I have read that U238 decaying into some Pb isotopes is still
the major mechanism although short-lived Al and other isotopes
would have contributed earlier in the earth's life.

Edit: Andre's article above confirms some of this and gives a figure
for the amount of heat lost to space: 4.2x10^13 W.

roofcrash

what kids would understand if you tell them about isotopes and radio activity ?

DaveC426913

If they're not old enough to understand it in-depth, that doesn't mean you feed them misinformation.

roofcrash

I thought about that before posting my question, i understand what you mean but children can not be old unless they have aspenger syndrome or they are genetically modified.

mgb_phys

Partly true, the earth remelted early after it's formation(350-500Myr?) due to radioactive decay (mostly K-40) - since then it's largely just insulation.
I don't think the modern decay power input is significant - is it?

HotCells

For some maverick ideas on this subject, see the website...http://www.nuclearplanet.com/

Mech_Engineer

I think that looking for anti-radioactive propoganda in Bill Nye's show is ridiculous. It's a kid's science show, and what he said isn't strictly incorrect it's just simplified.

statphys

The two major radioactive nuclides are Uranium and Thorium both of which are present in reasonable(ish) concentrations.